This invention pertains to a system for determining the location of wireless devices.
A variety of systems have been proposed which call for the ability to locate an object. For example, for asset control, it would be desirable to locate objects (e.g., laptop computers) within the confines of an office building. It is also desirable to be able to locate a cellular phone user.
The Global Positioning System (GPS) is an example of a prior art system for determining the location that uses a number of fixed or known location receivers or transmitters. A GPS receiver determines its position by processing signals received from a plurality of known location. A disadvantage of GPS is that in urban canyons or within buildings, signals from GPS satellites may be occluded.
For tracking objects inside an office building or the like, one approach is to arrange a group of receivers at fixed locations within the building, and to attach a transmitter to each object that is to be located. The fixed receivers are connected to a central computer that serves to determine the location of each object based on signals received from one or more of the group of receivers. Unfortunately this type of system requires the substantial installed infrastructure including all of the fixed receivers, and wired connections between them and the base stations. Moreover, these systems do not provide precise determination of location. A precision of +/xe2x88x9225% of the fixed receiver spacing is typical.
The strength of a received signal can in principle be used to determine the distance between a transmitter and a receiver. Unfortunately, in practice it is found that uncertainties in channel attenuation greatly diminish the accuracy that can be achieved.
It would be desirable to be able to use devices, the positions of which are not known in advance to locate other devices. It would be desirable to able to locate devices with which direct communication cannot be established.
What is needed is a system and method for determining location that requires less installed infrastructure.
Particularly it is unfortunate that it is problematic to obtain a location reading inside buildings and urban canyons.
Therefore, what is needed is a system and method which overcomes the above-mentioned shortcomings of the prior art.